The nature and reality of the aphid clone: genetic variation, adaptation and evolution

1 When aphid clones and clonality are discussed, it is still often said that they are 'genetically identical', a statement for which there is no direct evidence, and certainly not for the entire genome. By contrast, there is a growing body of empirical data from the application of high resolution molecular (DNA) markers that aphid asexual lineages rapidly mutate and that, in some documented cases, this variation is selectable, either positively or negatively. 2 Although it is true that, in enclosed conditions (e.g. laboratory or field cage), a so-called clone as defined as the asexual progeny of a single foundress may be traceable, this is rarely if ever possible in the field without the use of genetic markers, and even then, usually only at a relatively few loci (multilocus genotypes, 'MLGs'). 3 The continued use of the term clone without qualification of its true nature and the reality of its interesting biology is likely to hamper a proper understanding of the ecology and evolution of these insects (which are interesting in their own right because of their complex life histories, but also because they are important as major pests globally, both by causing direct feeding damage and by transmitting pathogenic plant viruses and thereby leading to huge economic losses in the agricultural, horticultural and forestry industries). 4 In this short review, I provide evidence of what is now known about aphid clonality after the widespread use of molecular markers, comprising information mainly gained within the last 15 years or so. 5 The data demonstrate widespread adaptation and evolution, sometimes involving introgression and hybridization. Because of this new knowledge, our ideas of what constitutes a clone are in need of serious re-evaluation.